1. Technical Field
The present disclosure relates to a method and an apparatus using a power transistor in a fuel cell stack diagnostic system.
2. Background
Fuel cells are a type of power generation device that converts chemical energy of a fuel into electric energy, using an electrochemical reaction in a fuel cell stack, as opposed to burning the fuel into heat.
The fuel cells can be useful for supplying power to small-sized electric/electronic products as well as supplying power for industry, home, and vehicles.
For example, Polymer Electrolyte Membrane Fuel Cells, or Proton Exchange Membrane Fuel Cells (PEMFC), which have the highest power density among fuel cells, have been widely studied as a power supply for driving vehicles. PEMFCs have quick start time and power conversion reaction time due to a low operation temperature.
A PEMFC includes a Membrane Electrode Assembly (MEA) having a catalytic electrode layer, where electrochemical reaction is generated, attached to both sides of a solid polyelectrolyte membrane in which hydrogen ions move, a Gas Diffusion Layer (GDL) that uniformly distributes reaction gases and transmits generated electric energy, a gasket and a fastener that maintain air-tightness of the reaction gases and a coolant and appropriate fastening pressure, and a separator or Bipolar Plate that moves the reaction gases and the coolant.
When a fuel cell stack is assembled by putting the unit cells together, the combination of a MEA and a GDL, which are main parts, is positioned at the innermost portion of the cells, in which the MEA has catalytic electrode layers coated with a catalyst so that hydrogen and oxygen can react. An anode and a cathode are arranged on both sides of the polyelectrolyte membrane, respectively. The GDL, the gasket, and other components. are stacked in the outer area where the anode and the cathode are positioned.
A separator with flow fields through which reaction gases that include hydrogen as a fuel and oxygen or air as an oxidizer, are supplied and a coolant flows is positioned outside the GDL.
A plurality of unit cells is stacked, with the configuration as a unit cell, and then end plates for supporting a current collector, an insulating plate, and stacked cells are coupled to the outermost side, in which a fuel cell stack is achieved by repeatedly stacking and fastening the unit cells between the end plates.
The number of unit cells stacked should be enough to obtain the required potential for a vehicle. The potential generated by one unit cell is about 1.3V. A plurality of cells may be stacked in series to produce the power for driving a vehicle.
The fuel cell stack composed of a plurality of cells, as described above, requires diagnosis to check whether desired performance and/or status is maintained.
FIG. 1 schematically shows a conventional diagnostic fuel cell stack diagnostic system.
Referring to FIG. 1, a conventional diagnosis and heat management system for a fuel cell stack may include an alternating current injector 20 that injects a diagnostic alternating current into a fuel cell stack 10 and a diagnostic analyzer 30 that diagnoses the fuel cell stack by analyzing a change in alternating current due to the injection of the diagnostic alternating current.
A conventional fuel cell stack diagnostic system generally performs diagnosis through Total Harmonic Distortion Analysis (THDA) of a diagnostic AC signal. To perform THDA, the diagnostic analyzer 30 may include a harmonic analyzer.
When a diagnostic alternating current IAC is injected into the fuel cell stack 10 by the alternating current injector 20, the diagnostic alternating current IAC overlaps the current ISTACK of the fuel cell stack 10. Therefore, the diagnostic alternating current IAC is included in the current ILOAD flowing to a load 40.
While the current ISTACK of the fuel cell stack 10 and the diagnostic alternating current IAC of the alternating current injector 20 overlap each other and flow to the load 40, the diagnostic analyzer 30 diagnoses the status and/or a problem in the fuel cell stack 10 by detecting the voltage of the fuel cell stack 10. The diagnostic analyzer 30 may then perform frequency conversion on the detected voltage, and then analyze the result.
However, the alternating current injector 20 of the conventional diagnostic system necessarily includes a decoupling capacitor CT for preventing collision of the diagnostic alternating current and the direct current of the fuel cell stack 10, when applying the diagnostic alternating current to the fuel cell stack 10.
The decoupling capacitor CT of the alternating current injector 20 should have a considerably large capacity, because it is required to pass a low-frequency alternating current.
Accordingly, the decoupling capacitor CT of the alternating current injector 20 is implemented by connecting tens of small-capacity capacitors CN in parallel, such that it may have a problem in that the cost is high and the size is large.
Distortion of the diagnostic AC signal may be generated, when the diagnostic alternating current of the alternating current injector 20 passes through the decoupling capacitor CT, such that precise diagnosis may not be achieved.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure.